Field of the Invention
The present invention relates to a light-emitting apparatus and a display apparatus.
Description of the Related Art
“Local diming control” is a control used for a liquid crystal display apparatus. With the local diming control, light emission brightness values (light emission amount) of a plurality of light source units of a backlight unit are individually controlled based on the image data. By performing the local diming control, the contrast of the display image (image displayed on screen) can be improved.
In a case where the local diming control is performed, the dispersion of the degree of deterioration in each light source unit, the dispersion of temperature in each light source unit and the like are generated among the plurality of light source units. And the light from each light source unit depends on the degree of deterioration of the light source unit, the temperature of the light source unit and the like. Therefore in order to obtain a desired light from each light source unit, light from the light source unit is detected and the light emission of the light source unit must be controlled based on the detection value of the light from the light source unit.
To detect light from each light source unit, the light source unit must be continuously lit for a predetermined time or more. This predetermined time is, for example, the total of the response time of the optical sensor which detects light from the light source unit and the processing time of the processing circuit (e.g. microcomputer), which processes the output signal of the optical sensor, as depicted in FIG. 6. In concrete terms, the circuits of the optical sensor includes a resistor, a capacitor, an operational amplifier and the like, and the response time of the optical sensor includes the response time of the resistor, the response time of the capacitor, the response time of the operational amplifier and the like. The response time of the optical sensor can be defined as the “time required for the optical sensor to charge light”, or can be defined as the “time required for saturation of the detection value of the optical sensor” The processing time of the processing circuit is, in concrete terms, the time required for A/D conversion processing to convert the output signal (analog signal) of the optical sensor into a digital signal.
Now a case where a pulse signal, depicted in FIG. 7, is input to a light source unit and the light source unit emits light in accordance with the pulse signal, is considered. In this case, a value corresponding to the wave height value of the pulse signal (pulse amplitude) is acquired as the detection value of the optical sensor (detection value corresponding to the emission brightness of the light source unit). If a change in the degree of age deterioration of the light source unit, a change in the temperature of the light source unit and the like are not generated, and a predetermined time or longer lighting period (pulse width of the pulse signal) is set, the same value (value which does not depend on the lighting period) can always be acquired as the detection value of the optical sensor.
A prior art on the detection of light from the light source unit is disclosed, for example, in Japanese Patent Application Laid-Open No. 2014-241277. According to the technique disclosed in Japanese Patent Application Laid-Open No. 2014-241277, one frame period of the image data is divided into a plurality of sub-frame periods. Then for each of the plurality of frame periods, the lighting period of the backlight unit is independently set so that the blinking sensation of the backlight unit is reduced, and a lighting period, not less than a predetermined time, can be ensured. In concrete terms, in a case where the lighting period of a certain sub-frame is increased, the lighting period in the other sub-frames is decreased.
However, even if such a prior art as the technique disclosed in Japanese Patent Application Laid-Open No. 2014-241277 is used, light from the light source unit may not be detected (the detection value of the light from the light source unit may not be acquired).
For example, display apparatuses which can display images having a wide dynamic range are now receiving attention. The wide dynamic range is called “High Dynamic Range (HDR)”, an image having a wide dynamic range is called an “HDR image”, and a display apparatus that can display an HDR image is called an “HDR display apparatus”. In the HDR display apparatus, not only is the display brightness of white (brightness on screen) increased, but the display brightness of black is decreased as well. In order to decrease the display brightness of black, the lighting of the backlight unit is turned OFF, or the light emission brightness of the backlight unit is controlled to be a very low light emission brightness. Therefore a sufficiently long lighting period may not be ensured while maintaining the display brightness of black. As a result, light from the light source unit may not be detected.
Further, in recent years, a number of light source units included in a display apparatus is increasing to improve the contrast of the display image. By increasing the number of light source units, the time required for processing to individually detect the light from each light source unit increases. Therefore if a number of light source units is large, the temperature of the light source units changes before the detection of the lights from all the light source units completes, and the accuracy of the detection values drops.